My yarn stash is never the right size. I usually think I have too much yarn but on the other hand I often can't find a certain color. For instance, DH recently informed me that spruce green is his favorite color. I decided to make him some spruce green socks but couldn't find anything spruce green in any weight in my stash.
One thing I do want to stop doing is trying new brands of yarn. It is better for my type of knitting just to have several main brands in as many colors as I can muster in my budget. In fact I just bought a skein of Cascade 220 in all the brightest colors at the Webs anniversary sale. I think it goes through May so I'll probably do another order next month. It is currently $4.89 a skein which isn't too bad. I'd use Cascade 220 (the non-superwash version) exclusively because of the rich, saturated colors but it is more expensive than other worsted weight wools so I only buy it when it is on sale.